New research in mice may upend current ideas about how autoimmune diseases get started. After cancer and heart disease, the most common group of diseases in the US are autoimmune diseases, which occur when the immune system mistakenly attacks the body’s own organs, tissues, and cells. Autoimmune diseases can affect just about any part of the body, and more than 100 types have been identified so far (some of the most common include type 1 diabetes, rheumatoid arthritis, multiple sclerosis, lupus, psoriasis, thyroid diseases, and inflammatory bowel disease). Most have no cure, and so patients can face a lifetime of debilitating symptoms, loss of organ function, and even death. Yet despite how common and serious they are, much about autoimmune diseases remains a mystery. The conditions are steadily increasing in prevalence, particularly in the developed world, yet experts don’t know why. It’s also unclear why women are disproportionately affected, accounting for …